The present invention relates to a semiconductor device including a buffer coat film formed on a passivation film and a method for fabricating the same.
FIGS. 20A to 21B are cross sectional views taken along the line XX—XX in FIG. 22 and showing process steps for fabricating a known semiconductor device. FIG. 22 is a plan view showing a periphery region of a wafer in a process step shown in FIG. 21B with part of the periphery region being taken along the line XXII—XXII.
First, in the process step shown in FIG. 20A, a conductive film made of an aluminum alloy film is deposited above a wafer 302 on which semiconductor elements (not shown) such as transistors are formed and then a multilevel interconnect layer (not shown) is formed above the semiconductor elements, for example, by sputtering. Thereafter, the conductive film is patterned by lithography and dry etching so that bonding pads 304 are formed. Each of the bonding pads 304 is connected to the semiconductor element located below via an interconnect, a plug or the like. Next, a passivation film 306 made of a silicon nitride film is deposited above the wafer 302 by CVD (chemical vapor deposition), so as to cover the bonding pads 304. Thereafter, apertures 306a and 306b each having a predetermined shape are formed, by lithography and dry etching, in portions of the passivation film 306 located on each scribe line region 310 and each bonding pad 304, respectively.
Next, in the process step shown in FIG. 20B, a buffer coat film 308 of approximately 6 μm thickness made of a photosensitive material is formed above the substrate by a spin coating method. Thereafter, parts of the buffer coat film 308 respectively located on the bonding pads 304 and the scribe line regions 310 are removed by lithography, thereby forming apertures 308a. As a result, the buffer coat film 308 is left on regions of the passivation film 306 (transistor formation regions) each surrounded by a certain number of bonding pads 304.
Next, in the process step shown in FIG. 21A, a surface protection tape 312 is bonded to the top of the wafer, above which the buffer coat film 308 is formed, using adhesive paste 320 adhered to the rear surface of the surface protection tape 312. The adhesive paste 320 has a thickness of 15 μm.
Next, in the process step shown in FIG. 21B, the rear surface of the wafer 302 is polished using the surface protection tape 312 as a protection film until the wafer has a predetermined thickness. This polishing process is performed using polishing slurry obtained by dispersing abrasives into liquid, and the generated swarf is eliminated together with the polishing slurry.
Thereafter, after removing the surface protection tape 312, the scribe line regions 310 of the wafer 302 are scribed to divide the wafer into individual chips, and each chip is assembled into a semiconductor device.
However, it has been found that, in the above-mentioned known method for fabricating a semiconductor device, the polishing slurry, including the swarf generated in the rear surface polishing process step, adheres to the surfaces of the bonding pads located on the periphery region of the wafer, resulting in a decrease in the fabrication yield of the semiconductor devices. The inventors have found, as a result of their various studies, that the fabrication yield of the semiconductor devices is decreased due to the following action.
As shown in FIG. 21B, there exist gaps between the wafer 302 and the adhesive paste 320 in the aperture 308a regions provided in the buffer coat film 308. Therefore, as shown in FIG. 22, it is considered that the liquid including the swarf generated in the rear surface polishing process step permeates from the periphery of the wafer 302 toward the center of the wafer 302 along the gaps located in the apertures 308a in a permeating direction 316 shown by the arrow, and the permeating liquid adheres to the surfaces of the bonding pads 304.